The shore at Eype is littered with large boulders, several tons in weight, that have broken from the strata high on the cliff and then slip-slided down the lower mudstones and clays to the beach. They are all rocks belonging to the Jurassic Dyrham Formation. that includes a fascinating assortment of mudstones, sandstones, and limestones, some with ironstone nodules or carbonate concretions, and lots with fossils. I cannot with confidence identify the specific rock types illustrated in all the close-up photographs I took. It is quite a complicated geology at this coastal location. However, a general picture of the represented rock types follows. Fossils are found in more or less all the strata, ammonites are said to be common, but the ones I saw were mostly fragmentary shells and bullet-shaped belemnites
An accurate and up-to-date source of information about the geology of this locality is the British Geological Survey’s Geology of south Dorset and south-east Devon and its World Heritage Coast, published in 2011 by the Natural Environment Research Council. All the information that follows has been obtained from this book.
The Dyrham Formation is comprised of three members. At the base of the cliff is the Eype Clay Member which is a pale, blue-grey micaceous silty mudstone and shale. The base of the Eype Clay Member is marked by The Three Tiers about a metre thick with three prominent sandstone beds separated by shales and mudstones. Higher up is a band of calcareous nodules, the Eype Nodule Bed. At the top of the band is Day’s Shell Bed with a rich fauna of juvenile bivalves and gastropods.
Above the Eype Clay member is the Down Cliff Sand Member made up of silts and fine sands with thin lenticles of hard calcareous sandstone. At its base is a fossil-rich layer known as the Starfish Bed, with abundant brittle-stars. At its top is the Margaritatus Stone which is hard, grey, iron-shot limestone.
At the top of the Dyrham formation is the Thornecombe Sand Member, sitting on the Down Cliff Sand Member. The bottom-most layer is the blue-grey Margaritatus Clay, above which are yellow-weathering, heavily bioturbated sands, with several horizons of large rounded calcareously cemented concretions. There is an impersistent band of limestone running through the middle of this, and a shelly Thornecombiensis Bed sealed by sandy mudstone atop it.
So you can see that there are many different rock layers and types in the stratified cliff, often obscured by land slips, and it is quite difficult for an amateur like myself to correctly identify pieces of these strata when they are lying on the shore.
However, one noticeable feature in the beach boulders was the occurrence of bioturbation: this is defined as a disruption of sediment by organisms, seen either as a complete churning of the sediment that has destroyed depositional sedimentary structures, or in the form of discrete and clearly recognisable burrows, trails, and traces (trace fossils). The most easily recognisable trace fossils are the largish burrows of Crustacean Thalassinoides – which you can see in images 4 and 9.
Another phenomenon that is responsible for some of the more unusual colouration and patterning of the rocks, is the transformation of blue-grey rock to yellow by the weathering process on exposure to air, which oxidises iron minerals in the stone. Iron staining, iron nodules (often in association with fossil fragments), and veins of iron, also contribute to rich colour patterns both within and on the surface of the boulders. Sometimes the colours are exhibited as a thin outer layer that is exfoliating into abstract patterns of contrasting hues on the rock.
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Barnacles often settle higher on the shore than most other organisms. They are adapted to live part of their life, sometimes most of it, actually out of water – being able to get by on splashes of water that extend beyond the high-tide line.
The way that animals and plants are distributed across the shore is known as zonation. Zonation is generally accepted as meaning a vertical separation of different groups of organism, often into distinct bands of different colour when living on hard substrates, resulting from the tolerances of individual species to dessication, temperature, and wave action – otherwise termed ‘exposure’. The barnacles and mussels occupy the mid-shore level. Around the world, although the species differ, the same phenomenon is found, with zonation more clearly visible to the casual observer on steep exposed rocky shores.
An extreme example of this zonation can often be seen on the artificial structures of a waterfront harbour where wooden wharf-sides, timber pier pilings, and metal revetments substitute for rock surfaces on which organisms can settle. Many of these artificial substrates are vertical and therefore the zoning of the organisms may be exaggerated and clearer to see.
The pictures in this post show a pale band or stripe, made up almost entirely of cream-coloured sessile or acorn barnacles, naturally cemented onto harbour-side structures, sometimes wholly encircling them. A few common periwinkle gastropod molluscs move around the barnacles, feeding on the bio-film that accumulates on their shells. Fronds of spiral wrack and sea lettuce type of seaweed, both also fairly tolerant of exposure out of water, are sometimes scattered over the barnacle zone. The barnacles have special adaptations that allow them to survive dehydration at low water but they are none-the-less vulnerable to predating dog whelks at all stages of the changing tides.
Below the barnacle zone, a darker, almost black band, is composed of edible mussels attached by byssus threads. Mussels are less tolerant to air exposure than the barnacles so they survive best lower down where they are not out of the water for so long. They are a sitting target, though, for starfish which use their tube feet to sucker onto these bivalves, forcing them to open, and then everting and inserting their starfish stomach into the mollusc so that they can feed upon the living contents.
All these photographs were taken on the waterfront in Halifax, Nova Scotia. Most of the piers and jetties are still traditionally made of timber because it is such an abundant commodity in Canada. There are generations of timber structures: new; old and decaying; and derelict examples. All of these show the barnacle banding. So do the more recently built rusting metal revetments to the edges of the renovated wharves in the more developed areas.
Interestingly, many modern high-rise buildings in that location have been constructed right on the water’s edge where they are supported by foundations of steel piles driven deep down into the very hard metamorphosed bed-rock. The pilings can be seen projecting below the buildings on the waterside elevations, disappearing into the harbour water. Each white-painted column displays at its base a lower ring of black mussels and a higher ring of paler barnacles – the structures themselves being reflected in the seawater with an odd abstract effect.
COPYRIGHT JESSICA WINDER 2014
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We know there is Nature in the city but in Montreal this can be experienced on a large scale in the Biodôme which is a unique museum of environment. Live collections with more than 4,800 animals from 230 species and 750 plants species in four ecosystems from the Americas, each with a different climate – all under one roof.
To quote from the Lonely Planet guide to Montreal and Quebec City:
you can amble through a rainforest, explore Antarctic islands, view rolling lowlands or wander along the raw Atlantic oceanfront – all without ever leaving the building.
Penguins frolic in the pools…the tropical chamber is a cross-section of Amazonia with mischievous little monkeys teasing alligators in the murky waters below. The Gulf of St Lawrence has an underwater observatory where you can watch cod feeding alongside lobsters and sea urchins in the tidal pools. The appearance of the Laurentian Forest varies widely with the seasons, with special habitats for lynx, otters and around 350 bats.
[These pictures from the visit to the Biodôme are also shown on my other WordPress site along with more postings of photographs taken in Montreal during my trip to Canada last year].
The Chinese Garden at Jardin Botanique de Montreal in Canada was inaugurated in 1991 and inspired by the magnificent private gardens of the Ming Dynasty (14th to 17th century) and is considered the largest of its kind outside of China.
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A cold and rainy day in March saw me exploring a beach on the west coast of Ireland in Galway Bay, between Galway City and Salthill. Braving the inclement weather were joggers, plugged-in to headphones and clutching water bottles, as they ran along the promenade at the top of the shore. One or two individuals strolled with raincoats flapping and umbrellas braced against the wind. I had the seashore itself more-or-less to myself.
It is a sheltered, gently sloping, sandy shore where coloured pebbles accumulate at the top of the beach. Line after line of boulders, like loosely constructed groynes, stretch from high to low water mark dividing the shore into sections. They remind me of the stone walls that seem to proliferate in countryside and hill slopes all along this coast. Each beach section is like a field where mid- to low-shore rocks anchor a crop of seaweed – a profusion of vegetation that drapes each boulder and spreads out to blanket the surrounding sand.
The cloud-filled sky and persistent rain make the beach seem, from a distance, dull, almost monochromatic and melancholic – but that is an illusion. Close up, the limestone and granite pebbles provide a mosaic of many colours, intensified by the wetness. The seaweeds are made up of many types with a range of hues. Golden yellow fruiting bodies, and fronds in shades of olive, mark out the dominant Egg Wrack (Ascophyllum nodosum). Finely-branched red Wrack Siphon Weed (Polysiphonia lanosa) contrasts with the Egg Wrack on which it grows epiphytically. Darker greens and browns are typical of the smaller Bladder Wrack (Fucus vesiculosus). Short curling clumps of greenish-yellow early-stage Channel Wrack (Pelvetia canaliculata) are distinct. Both limpet shells and mussel shells show patches of dark brown encrusting algae (probably Brown Limpet Paint, Ralfsia verrucosa). The seaweeds splash colour across rocks, pebbles and sand. – and the rocks themselves originate from different locations, sedimentary or igneous, with their own subtle colouring, texture and patterns.
How different this scene must look when the tide is in and the seaweed can float upright and sway in the waves. It really must look like an underwater field. The Egg Wrack (growing up to a metre and a half long) has egg-sized and egg-shaped air bladders, one formed every year along each frond, to aid buoyancy. The much shorter Bladder Wrack has small rounded air bladders in pairs either side of the midribs to help it float.
When the intertidal shore is submerged, acorn barnacles (Cirripedia) and edible mussels (Mytilus edulis) attached to the rocks can filter food particles from the water. The huge numbers of large limpets and common periwinkles living amongst and feeding upon the seaweed, and grazing red and yellow biofilms that encrust the rocks, can move far more easily and for greater distances when buoyed up by water and there is no danger of dessication – although they can be active when exposed to air at low tide if conditions remain cool and moist.
COPYRIGHT JESSICA WINDER 2014
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